Use github actions for building images

[teeks99]

Make a method for an automatic (cron, weekly) and manual (push) to rebuild images and push to docker hub using the github actions infrastructure.

[krlmlr]

When building on GitHub Actions, pushing to GitHub Packages works out of the box. See https://github.com/cynkra/docker-images/tree/main/.github/workflows for actions that might just work here, with minimal adaptation.

[krlmlr]

Example run: https://github.com/krlmlr/gcc-ubuntu-docker/actions/runs/12948600838 .